Magnetic nanoparticles, in particular iron oxide particles, are employed in medicine for a number of applications including drug delivery and hyperthermia, and can be used as contrast agents in magnetic resonance imaging (MRI). The researchers of the BIAM have developed a hybrid system based on magnetite nanoparticles and the polypeptide polyarginine (polyR-Fe₃O₄). The particles exhibit low toxicity, comparable to that of Resovist®, a contrast agent commonly used for MRI.

The studies conducted on the use of polyR-Fe₃O₄ in MRI have shown that the image resolution obtained is 1.6 times higher than with currently used agents.

These hybrid nanoparticles can also be used to locally generate hyperthermia, for example for tumor therapy, with a specific heating power of 208 watts per gram for the hybrids as compared to 83 watts per gram for Feridex®, another agent used in this type of treatment.

Finally, therapeutic molecules were grafted onto the polyR-Fe₃O₄ surface, and then transported in the body. Polyarginines in particular have the capacity to cross cell membranes, thereby offering additional development opportunities.

The polyR-Fe₃O₄ hybrid nanoparticles thus possess multiple talents: they can be used as contrast agent for MRI, as therapeutic agent for hyperthermia and as a delivery vector in targeted areas of a cell or a tumor. These properties make polyR-Fe₃O₄ a theranostic agent (a contraction of the words 'therapy' and 'diagnostic') and a prime candidate for Magnetic Particle Imaging, which is still in development but offers instantaneous images of soft tissues with the highest possible resolution.